Diffusion of sensitizing dyes in photographic emulsions



Patented Dec. 7, 1943 UNlTED STATES PATENT ()FFICE DIFFUSION FSENSITIZING DYES IN PHOTOGRAPHKC EMULSIONS No Drawing. Application May1, 1941, Serial No. 391,375. In Great Britain June 6, 1940 Claims.

This invention relates to the diffusion of sensitising dyes inphotographic emulsions and more particularly to the retardation of suchdiffusion.

For certain purposes in photography, there are required sensitivepapers, films, plates and similar materials comprising two or moreemulsions which respond in diiferent ways to differently colored light.Thus, one of the emulsions may be insensitive to light of a color towhich a second emulsion may be sensitive. In the production of thesesensitive materials, the emulsions are sometimes mixed beforeapplication to the support, while in other instances, the emulsions areapplied successively in layers to the support. For example, it is commonpractice in the production of sensitive materials for use in colorphotography to apply successively to the support layers emulsionssensitive to different regions of the spectrum. In certain instances, incolor photographic elements, two or more emulsions are mixed together inone layer.

As a further example of the use of sensitive materials comprising two ormore emulsions which respond in different ways to diiierently coloredlight, may be mentioned printing papers which are capable of giving aresult of high or low contrast, depending upon the color of the lightused in printing. Such papers can be produced by applying to a papersupport a mixture of twoemulsions, one of which gives an image of highcontrast and can be printed by using light of one color, and the secondgives an image of low contrast and can be printed by using a light ofdifferent color. Instead of a mixture of two emulsions, the emulsionscan be applied successively to the paper support. The emulsion used insuch printing papers, or in the aforementioned color photographicmaterials, may be all of one type, say silver chloride or silverbromide, or the emulsions may be of difierent types.

Whether the emulsions are of the same or of diilerent types, thedifferent sensitivities of the emulsions to differently colored lightcan be con trolled by means of sensitizing dyes. Thus, one emulsion maybe prepared free from sensitizing dye and hence sensitive to blue lightbut not to light of longer wavelengths, while the other emul sion maycontain a dye which sensitises the emulsion. to yellow light, in whichcase the second emulsion will be sensitive both to yellow and to bluelight, since the emulsion possesses a natural sensitivity to blue.Alternatively the two emul sions may contain different sensitising dyes,so that each emulsion is dye-sensitised for a different spectral region.

Numerous sensitising dyes which may be employed are known, includingamong others, sensitising dyes from the cyanine, the hemicyanine, themerocyanine, the oxonol and the hemioxonal dye classes. In practice,however, the sensitising dye or dyes adsorbed on the grains of oneemulsion have a greater or lesser tendency to wander or diffuse to thegrains of another emulsion where the dye is not desired. When the grainsof the two emulsions are adjacent, that is sufficiently close, forexample when the emulsions are mixed or coated in immediate contact oneon the other; such difiusion occurs almost solely during the time inwhich the emulsions are adjacent in the wet condition. If such diffusionoccurs the initial difference in sensitivity between the emulsions is,of course, reduced, and may even be lost practically entirely. Evenwhere the emulsions are applied in consecutive layers, the tendency ofcertain dyes to wander from one layer to another is very marked; Only arelatively few of the well-known powerful sensitising dyes have lowenough resistance to wander to be useful in the production ofphotographic materials of the kind described above.

.To reduce this undesirable tendency to wander, it has been proposed tointroduce into the molecules of the sensitising dyes, longchain organicgroups. Dye molecules containing such chains show a lesser tendency todiffuse, but such dyes also show a greater or lesser decrease insensitising power, depending upon the point of attachment of thelong-chain organic group. At best, such a method of retarding diffusionis at the expense of sensitising power. It has also been proposed toretard wandering of quaternary salt types of sensitising dyes inphotographic emulsions by incorporating perchlorates, such as sodiumperchlorate, in the emulsions containing the dyes. However, this methodleaves much to be desired, and in the case of non-quaternary salt typesof dyes, such as merocyanine dyes, the method is of no utilitywhatsoever.

It is accordingly an object of my invention to provide a process forretarding such difiusion of sensitising dyes. Another object is toprovide emulsions containing sensitising dyes which are retarded fromdiffusion. Other objects will become apparent hereinafter.

I have found that the tendency for sensitising dyes of all types, andparticularly dy'es of the above-mentioned types, to wander or diffusefrom the grains of one photographic silver halide emulsion, to thegrains of an adjacent silver halide emulsion, can be substantiallyreduced by dispersing in the emulsion a substantially waterinsolublemetal compound preferably before bringing the emulsions into contact andalso preferably after the sensitising dye. I have found thatsubstantially water-insoluble metal oxides, metal hydroxides, metaloxysalts and metal hydroxysalts are advantageously employed.

In practicing my invention, to obtain the best results the followingconditions should be observed. It is important that such water-in- Inthe case of each water-insoluble compound tested some of the mixedemulsion was coated immediately after the mixing and then dried whilesome was coated after being kept in the wet condition at 35 C. Somecompounds were found to prevent wandering even under the latter rathersevere test conditions while others were satisfactory for immediatecoating but showed a little Wandering after the two hours keeping in thewet condition. The dye-wandering was observed soluble metal compoundshould be incorporated by means of wedge spectrograms. The followin theemulsion before it is brought into contact ing table shows the effectsobtained:

Table in bl 7 i t Watersolu e metal go a in compound Effect on wander ngEffect on speed suwem i sion Stops wandering No change Reduceswandering. Slight speed loss in dye-sensitised emulsion do No change .doNo cihangc (loss in gamma) Almost stops wandering Reduces wandering doAlmost stops Wandering Increase of speed of dye-sensitised emnlsionLowdcrs gamma o Great increase in speed of dye-sensitised emulsion;

slight increase in speed of unsensitised emulsion.

do .do d .do Great increase in speed of dye-sensitised emulsion; slightincrease in speed of unsensitised emulsion (tends to fog). ReducesWandering consid- No change 4. 8

erably. i Al (OH) OGOH 2.. Reduces wandering Lowers gamma o1unsensitised emulsion 4.0 BaSO; do No change 6.0

with another emulsion. Where it is desired that two adjacent emulsionsshould, both be sensitized but with different dyes then each emulsionshould be sensitised and have incorporated in it a water insoluble metalcompound before the two emulsions are brought into contact. TheWater-insoluble metal compound can be added to the emulsion in the formof a finely divided powder or precipitate. More advantageously however,the water-insoluble metal compound is first emulsified in a 5 per centsolution of gelatin in water, the emulsification being followed. bycentrifuging to remove all but the finest grains of water-insolublecompound. A suspension of the water-insoluble metal compound can also beformed by precipitation of the water-insoluble metal compound in agelatin solution. However prepared, such a gelatin suspension of thewaterinsoluble metal compound provides an advantageous form in which toadd the water-insoluble metal compound to the emulsion. Thewaterinsoluble metal compound should, of course, be thoroughlyincorporated throughout the emulsion.

The concentration of the water-insoluble metal compound which is mostadvantageously employed will depend, of course, upon the silver halideemulsion employed and upon the sensitising dye employed. Ordinarily,however, from about to about 150 grams of water-insoluble metal compoundper gram-mole of silver halide in the emulsion will suilice to retardwandering of the sensitising dyes to an adjacent emulsion.

The following procedure was found satisfactory to determine the effectof the various waterinsoluble metal compounds. To a hard silver chlorideemulsion was added a green sensitising dye and the emulsion was held at35 C. for minutes. A gelatin suspension of the water-insoluble compoundwas then added, and this was followed by a blue sensitive soft bromideemulsion.

silver bromide developing-out emulsion.

Zinc oxide is the most eihcacious of the materials listed in the abovetable. After two hours keeping in the wet condition at 35 C. of themixed emulsion containing zinc oxide, there was no wandering of thesensitising dyes. The lower the colour sensitivity of the emulsioncompared with the natural blue sensitivity of the other emulsion, thegreater is the necessity to use Water insoluble compounds which arehighly efficacious, using if necessary also a water insoluble resin toimprovethe efiect still further. As shown in the copending applicationof Edward P. Davey, Serial No. 387,437, filed April 8, 1941,incorporation of water-insoluble resins in photographicgelatino-silver-halide emulsions not earlier than the sensitising dyes,serves to retard diffusion of the sensitising dyes. Thus, from about 10to about 35 grams of resins, such as whole shellac, soft shellac, hardshellac, hydrolised shellac, colophony, dammar, sandarach, mastic orglyptals, per gram-mole of silver halide in the emulsion serves toretard diffusion of sensitising dyes. I have now found with a mixture ofmy water-insoluble metal compounds and substantially waterinsolubleresins, e. g.,' those set forth above, that the components of themixture co-operate to retard diffusion of sensitising dyes in a highlyefficacious manner.

The following example will serve to illustrate the practice of myinvention.

Example 1 Two gelatino-silver-halide emulsions were selected, the onebeing a hard silver chloride developing-out emulsion and the other beinga soft The silver ratio of the two emulsions was one to one. The pH ofeach emulsion was adjusted to 7:0. The chloride emulsion was sensitisedwith 5-[( ethyl-2(3) benzoxazolylidene) ethylidenel-3-ethyl-1-phenyl--2-thiohydantoin. The sensitised emulsion was allowed tostand at 35 C. for 30 minutes. To this sensitised emulsion, whichcontained the equivalent of 200 grams of silver nitrate, were then addeda gelatin suspension of 20 grams of magnesium oxide followed by 30 gramsof soft shellac resin contained in ethyl alcoholic solution per cent byweight of resin). The resulting mixture was kept at 35 C. for a periodof time, depending upon the final chloride speed desired (say for 90minutes). To the soft bromide emulsion were added the same amounts ofmagnesium oxide and resin. The two emulsions were then mixed. The mixedemulsion can be coated immediately or after standing, say for one hour.

Apart from the fact that the oxides of magnesium, calcium and lanthanumretard sensitising dye difiusion, these oxides cause a substantial risein the speed of the dye-sensitised emulsion. This speed rise isdependent upon two factors, (1) the ratio of oxide to silver in theemulsion and (2) the time of keeping of the dyesensitised emulsion inthe liquid state with the oxide, before coating. There i a gradual speedrise over a period of several hours until the emulsion runs into stain.The hydroxides of calcium, magnesium and lanthanum function in the sameway, and probably the effect of the oxides is due to their becominghydrated to the corresponding hydroxides. While these oxides andhydroxides are substantially water-insoluble, they are slightly solublein water and, therefore, give the emulsions a high pH. The speedincrease due to this high pH, however, is very slight.

In general from about to about grams of the oxides or hydroxides ofcalcium, magnesium or lanthanum per gram-mole of silver halide willsubstantially retard diffusion without greatly affecting speed, whereasfrom about 75 to about 125 grams per gram-mole of silver halide will notonly substantially retard diffusion of the sensitising dyes, but willconsiderably increase the speed of the dye-sensitised emulsion.

With the oxides and hydroxides of calcium, magnesium and lanthanum, thesensitising dyes should be selected with especial care, since thesesubstances tend to decompose some sensitising dyes upon standing withthem.

Since the refractive indices of magnesium hydroxide and certain glyptalresins are almost the same as that of gelatin, clear films can beobtained when employing a combination of these two substances.

For best results, I have found that the hard chloride emulsions employedshould contain an excess of soluble chlorides.

In accordance with a further embodiment of my invention, I incorporatein the emulsions along with the water-insoluble metal compound,

a water soluble metal salt of a resin. The waterinsoluble metal compoundand the water-soluble metal salt of the resin co-operate to retarddifiusion of the sensitising dyes in an efficacious manner. Watersoluble metal salts of resins which are advantageously employed are thealkali metal or ammonium salts of resins, such as whole lac, hard lac,soft lac, hydrolised lac, colophony, dammar, sandarach, mastic andglyptals.

In accordance with a still further embodiment of my invention, I retarddiffusion of sensitising dyes from the grains of one photographicgelatino-silver-halide emulsion to the grains of another adjacentemulsion by incorporating in Water soluble metal salts Water solublemetal or hydroxides salts or resins Any Water soluble salt Ammonium oralor hydroxide ofkali metal (e. g.,

Aluminium potassium or so- Barium dium) salts of- Cadmium Whole lacCalcium Hard lac Cerium Soft lac Cobalt Hydrolysed lac Copper OolophonyMagnesium Dammar Manganese Sandarach Strontium Mastic Thorium GlyptalsZinc In carrying out my invention according to the preferred embodiment,I first adjust the pH of the gelatino-silver halide emulsion to at least7. To the sensitised emulsion I then add a one percent aqueous solutionof the water-soluble metal salt or hydroxide followed by a 5 per centaqueous solution of the Water soluble metal saltcf a resin, Sufficientof the two solutions are incorporated to give from about 10 to aboutgrams of water-insoluble metal salt of a resin per gram-mole of silverhalide in the emulsion.

The following example will serve to illustrate the practice of myinvention.

A hard gelatino-silver-chloride developing-out emulsion sensitised with5-[3-ethyl-2(3)'-benzoxazolylidene) -ethylidenel-3-ethyl-1-phenyl 2thiohydantoin containing the equivalent of 200 grams of silver nitratewas adjusted to a pH of at least '7. To the resulting emulsion wereadded a 1 per cent aqueous solution of 5 grams of cadmium nitrate. Thecadmium nitrate was thoroughly incorporated in the emulsion, and a slowstream of a 5 per cent aqueous solution of 30 grams of the sodium saltof colophony were added. After a wait of 15 minutes, a softgelatino-silver-b-romide developing-out mulsion was mixed with thechloride emulsion. Such a mixed emulsion can be kept at 35 C. for somehours without dye wandering into the grains of the other emulsion. It ispreferable to incorporate also in the soft bromide emulsion awater-insoluble metalsalt of a resin in the same manner as described forthe hard chloride emulsion.

Instead of cadmium nitrate, 5 grams of zinc chloride or 5 grams ofcobalt ammonium sulfate were found to give good results. Likewise, thesodium salt of colophony was replaced with the sodium salt of soft lacresin in connection with cadmium nitrate, zinc chloride and cobaltammonium sulfate, and efiicacious retardation of diffusion of thesensitising dye was obtained.

In accordance with any of the embodiments of my invention, diffusion ofsensitisin'g dyes from the cyanine class, the merocyanine class (see U.S. Patent 2,078,233, dated April 27, 1937),

the hemicyanine class (see U. S. Patent 2,166,736, dated July 18, 1939),the hemioxonal class (see U. S. Patent2,216,4ll, dated October 1, 1940),and the oxonal class (see the copending application of L. G. S. Brookerand G. H. Keyes, Serial No. 27G,9l6, filed April 29, 1939) can beretarded.

What I claim and desire to be secured by Letters Patent of the UnitedStates is:

l. A photographic element comprising at least two photographic silverhalide emulsions positioned with the grains of one emulsion adjacent tothe grainsof another emulsion, at least one of said emulsions beingsensitized with a sensitizing dye, at least theemulsions sensitized witha sensitizing dye containing a substantially water-insoluble metalcompound selected from the group consisting of metal oxides, metalhydroxides, metal oxysalts, metal hydroxysalts and metal salts ofresins, to retard difiusion of the sensitizing dye, said metal compoundhaving been incorporated in the emulsion after the sensitizing dye.

2. A photographic element comprising at least two photographic gelatinosilver halide emulsions positioned with the grains of one emulsionadjacent to the grains of another emulsion, at least one of saidemulsions beingsensitized with a sensitizing dye, at least the emulsionssensitized with a sensitizing dye containing a substantiallywater-insoluble metal compound selected from the group consisting ofmetal oxides, metal hydroxides, metal oxysalts, metal hydroxysalts andmetal salts of resins, to retard diffusion of the sensitizing dye, saidmetal compound having been incorporated in the emulsion after thesensitizing dye.

3. A photographic element comprising at least two photographic gelatinosilver halide emulsions positioned with the grains of one emulsionadjacent to the grains of another emulsion, at least one of saidemulsions being sensitized with a sensitizing dye, at least theemulsions sensitized with a sensitizing dye containing a substantiallywas ter-insoluble metal compound selected from the group consisting ofcalcium, magnesium, lanthanum and zinc oxides and hydroxides, to retarddiffusion of the sensitizing dye, said metal compound having beenincorporated in the emul sion after the sensitizingdye.

4. A photographic element comprising at least two photographic gelatinosilver halide emulsions positioned with the grains of one emulsionadjacentto the grains of another emulsion, at least one of saidemulsions being sensitized with a sensitizing dye, at least theemulsions sensitized with a sensitizing dye containing a substantiallywater-insoluble metal compound selected from the group consisting ofmagnesium hydroxide and magnesium oxide, to retard diffusion of thesensitizing dye, said metal compound having been incorporated in theemulsion after the sensitizing dye.

5. A photographic element comprising at least two photographic gelatinosilver halide emulsions positioned with the grains of one emulsionadjacent to the grains of another emulsion, at least one of saidemulsions being sensitized with a sensitizing dye, at least theemulsions sensitized with a sensitizing dye containing a substantiallywater-insoluble metal compound selected from the group consisting ofzinc hydroxide and zinc oxide, to retard diffusion of the sensitizingdye,

sitizing dye.

7. A- photographic element comprising at least two photographic gelatinosilver halide emulsions positioned with the grains of one emulsionadjacent to the grains of another emulsion, at least one of saidemulsions being sensitized with a sensitizing dye, at least theemulsions sensitized with a sensitizing dye containing, in aconcentration of from about 10 grams to about 156 grams per gram-mole ofsilver halide in the emulsions, a substantially water-insoluble metalcompound selected from the group consisting of metal oxides, metalhydroxides, metal oxysalts, metal hydroxysalts and metal salts ofresins, to retard diffusion of the sensitizing dye, said metal compoundhaving been incorporated in the emulsion after the sensitizing dye.

8. A photographic element comprising at least two photographic gelatinosilver halide emulsions positioned with the grains of one emulsionadjacent to the grains of another emulsion, at least one of saidemulsions being sensitized with a sensitizing dye, at least theemulsions sensitized with a sensitizing dye containing a substantiallywater-insoluble metal compound selected from the group consisting ofmetal oxides, metal hydroxides, metal oxysalts, metal hydroxysalts andmetal salts of resins, and containing a substantially water-insolubleresin, to retard diliusion of the sensitizing dye, said metal compoundand said resin having been incorporated in the emulsion after thesensitizing dye.

9. A'photographic element comprising at least two photographic gelatinosilver halide emulsions positioned with the grains of one emulsionadjacent to the grains of another emulsion, at least one of saidemulsions being sensitized with a sensitizing dye, at least theemulsions sensitized with a sensitizing dye containing a substantiallywater-insoluble metal compound selected from the group consisting ofcalcium, magnesium, lanthanum and zinc oxides and hydroxides, andcontaining a substantially water-insoluble resin, to retard diffusion ofthe sensitizing dye, said metal compound and said resin having beenincorporated in the emulsion after dye.

10. A photographic element comprising at least two photographic gelatinosilver halide emulsions positioned with the grains of one emulsionadjacent to the grains of another emulsion, at least one of saidemulsions being sensitized with a sensitizing dye, at least theemulsions sensitized with a sensitizing dye containing magnesium oxideand soft lac resin, to retard difiusion of the sensitizing dye, saidmagnesium oxide and soft lac resin having been incorporated in theemulsion after the sensitizing dye.

11. A photographic element comprising at least two photographic gelatinosilver halide emulsions positioned with the grains of one emulsion thesensitizing adjacent to the grains of another emulsion, one of saidemulsions being sensitized with a merocyanine dye and containingmagnesium oxide and soft lac resin to retard diffusion of thesensitizing dye, said magnesium oxide and soft lac resin having beenincorporated in the emulsion after the merocyanine dye.

12. A photographic element comprising a contrasty gelatino silverchloride emulsion sensitized to the green with a sensitizing dye, and asoft gelatino silver bromide emulsion positioned with its grainsadjacent to the grains of the contrasty chloride emulsion, both thechloride and the bromide emulsion containing magnesium oxlde and softlac resin to retard diffusion of the i.

dye-sensitized emulsion a substantially water-insoluble metal compoundselected from the group consisting of metal oxides, metal hydroxides,metal oxysalts, metal hydroxysalts and metal salts of resins, and thenbringing the two emulsions into contact.

14. A process for preparing a photographic element comprisingincorporating in at least one of two photographic gelatino silver halideemulsions, prior to bringing the emulsions into contact, a sensitizingdye, and after incorporation of the sensitizing dye in the emulsion,incorporating in at least the dye-sensitized emulsion a substantiallyWater-insoluble metal compound selected from the group consisting ofmetal oxides, metal hydroxides, metal oxysalts, metal hydroxysalts andmetal salts of resins, and then bringing the two emulsions into contact.

15. A process for preparing a photographic element comprisingincorporatingin at least one of two photographic gelatino silver halideemulsions, prior to bringing the emulsions into contact, a sensitizingdye, and after incorporation of the sensitizing dye in the emulsion,incorporating in at least the dye-sensitized emulsion a substantiallywater-insoluble metal compound selected from the group consisting ofmetal oxides, metal hydroxides, metal oxysalts, metal hydroxysalts andmetal salts of resins and then bringing the emulsions into contact.

EDWARD B. KNOTT.

